In the disposable medical equipment field, various biomedical sets such as the Travenol AV Fistula Cannulation Set and other hemodialysis blood sets require certain rigid parts such as the female luer adaptor, which must be bonded to the polyvinyl chloride tubing.
Accordingly, the rigid material which would be desired should be injection-moldable without brittleness, resistant to contact with alcohol without cracking or crazing, and solvent bondable, particularly to polyvinyl chloride plastic materials. Also, the material should be stable in the presence of ethylene oxide gas and radiation to permit sterilization by those techniques.
A copolyester material known as poly(ethylene cyclohexanedimethylene terephthalate) is sold by the Eastman Kodak Company, for example, under the trademark KODAR PETG 6763. This material is basically a polyester of polyethylene terephthalate, modified with a diol product which is also sold by the Eastman Kodak company under the name of cyclohexanedimethanol, having a number average molecular weight of about 26,000. The copolymer material bonds to the plasticized polyvinyl chloride plastic well, but it exhibits certain processing and other problems.
For example, the KODAR PETG 6763 material can be injection-molded at temperatures above 390.degree. F.. However, at temperatures of 420.degree. F. and above, the material degrades, making it brittle. This results in a difficult injection-molding process, since the molding range is quite narrow. Also, at the low end of the molding range or below, the plastic becomes brittle because of molded-in stress.
As a result of this, in the molding work which we were involved with concerning the KODAR material, certain lots of the molded luer adaptors proved to be unduly brittle, and also when contacted with alcohol tended to crack, in view of high molding stresses present in the material.
In accordance with this invention, an improved composition is provided which exhibits good bonding characteristics toward polyvinyl chloride plastics, yet which also is much tougher than the previously discussed material, and is much less likely to form intermittent cracks in the presence of alcohol.
Furthermore, the material of this invention can be injection-molded at temperatures as low as 360.degree. F., and has a higher degradation temperature of about 430.degree. F., which permits continuous and reliable commercial scale injection molding processes without encountering the occasional brittleness that was previously encountered.
Interestingly, the material of this invention as it is formed is not formed in a single phase, but has a pearlescent look about it, implying a certain phase incompatibility (i.e., multiple phases) between the ingredients. Nevertheless, and most surprisingly, the physical properties of these materials remain good although it would be normally predicted from this that the physical properties would be poor.